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Table 2 If then rules
IF X1 IS MEDIUM SMALL THEN Y1 IS VERY SMALL
AND Y2 IS MEDIUM LARGE
IF X1 IS MEDIUM THEN Y1 IS SMALL AND Y2 IS
MEDIUM
IF X1 IS MEDIUM LARGE THEN Y1 IS MEDIUM AND Y2
IS MEDIUM SMALL
IF X1 IS LARGE THEN Y1 IS LARGE AND Y2 IS SMALL
IF X1 IS VERY LARGE THEN Y1 IS VERY LARGE AND
Y2 IS VERY SMALL
8.1 Coding of Fuzzy Rule
In this proposed method fuzzy if-then rules are coded as GFS method with mem-
bership function according to Fig.
8
(Kasiri et al.
2011a
,
2012a
). This innovative
membership function is suited for the determination of better rules.
8.2 De
nition of Fitness Function
A particular type of objective function that prescribes the optimality of a solution
(that is, a chromosome or string) in a genetic algorithm is
fitness function. Hence
that particular string may be ranked against all the other strings. Optimal strings, or
at least strings which are more optimal, are allowed to create and compound their
datasets by any of several
techniques, producing a new generation that will
hopefully be even better.
Fitness function in FRENGA includes two parts; one of them compares gen-
erated rules with optimal values, thus a rule that covers most of the best values
could be a desired rule. In another part; numeral equivalent of rules are being
calculated on wind turbine power formula, thus these rules calculated on MLP NN
either, consequently a rule that least slide from trained neural network value could
be a good rule. Finally, for each piece of these parts has been allocated a weight. As
a result the best rules have selected from initial random rules. Figure
9
shows block
diagram of the FRENGA controller (Kasiri et al.
2011a
,
2012a
).
8.3 Simulation Results of FRENGA
Figure
10
a reveals Tip-Speed Ratio of wind turbine. Figure
10
b shows the pitch
angle response. It is corroborated that the pitch actuator does not suffer from
excessive activity despite the strong turbulence.
Figure
10
c shows the evolution of the controlled torque of wind turbine in Pu
that is controlled by FRENGA. The turbine is required to operate at its rated power.
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